This invention relates to dispensing apparatus for use with pressurised dispensing containers and in particular, but not exclusively, for apparatus for dispensing orally inhaled medicinal products in aerosol form.
Various means have been proposed to synchronise the release of an aerosol product into a mouthpiece of a dispensing apparatus in a manner which is synchronised with the inhalation of breath by a user. Such synchronisation is important in ensuring that as much as possible of the dispensed dose reaches the lungs of the user. This is of particular importance when administering drugs for the relief of asthma.
It has been proposed in GB 1392192 to provide a pivoted vane mechanism to sense air flow and release the aerosol product as a result of the user""s inspiratory effort. Such a mechanism is difficult to manufacture to the required tolerance for controlled and repeatable performance in oral inhalation due to difficulties in moulding and distortions appearing in the moulded elements. There remains a need to provide a practical solution which will be suitable for production on a commercial scale.
It is known from U.S. Pat. No. 4,576,157 to provide dispensing apparatus comprising a housing defining a socket for receiving, in use, a pressurised dispensing container of the type having a tubular valve stem biassed into an extended position and having first valve means operable to dispense fluid through the stem when the stem is depressed. The housing defines an airway extending from an inlet means, which is open to the atmosphere, to an outlet defined by a mouthpiece. Inhalation by a user results in an air flow through the airway. The apparatus further comprises an actuator, in which the stem is sealingly received in use such that the actuator and the stem together define a first chamber into which fluid is dispensable by operation of the first valve means. A second valve means normally closes the chamber and is actuatable to release fluid from the first chamber to flow into the airway. The second valve means comprises a valve member located externally of the first chamber and co-operable with a valve seat of the actuator. A flow sensor is arranged in the airway and operable to actuate the second valve means in response to a flow of air being sensed in the airway. The flow sensor is movable in response to the flow of air in a bore defined by the housing between first and second positions corresponding to closed and open conditions of the second valve means respectively. The flow sensor is connected directly to the valve member and provided with biassing means urging the flow sensor into the first position, in which the valve member is biassed into sealing contact with the valve seat.
It is further known from EP 0476991 to provide a dispensing apparatus in which a flow sensor is provided comprising a piston, which is axially movable in the bore, and guide means operable to guide the movement of the piston so as to maintain a lateral surface of the piston in spaced relationship from a side wall of the bore. A passageway is thus defined having a cross-section which is substantially uniform throughout the travel of the piston between the first and second positions. The passageway, constituting a constricted portion of the airway, presents a substantially uniform impedance to the flow of air throughout the movement of the piston. As the user inhales, a pressure drop is developed across the flow path. This pressure drop acts on the piston to define a force which is used to operate the device.
An advantage of this arrangement is that the user experiences a constant impedance to the inhaled air flow throughout the inhalation process resulting in a slow and steady flow of air in which the atomised medicament is carried. Such a characteristic of flow rate has proved to be highly beneficial to the effective deposition of inhaled medicaments where deposition of an atomised spray in the user""s lungs is intended. In contrast, any discontinuity in the flow rate resulting from a change in impedance can result in a rapid increase in flow rate with consequent early deposition of the medicament in the throat or mouth of the user. A further advantage is that the uniformity of flow avoids any xe2x80x9cdead spotxe2x80x9d in the flow characteristic during which the user is prevented from receiving inhaled air, thereby avoiding unnecessary distress for the user who may for example be an asthmatic.
A disadvantage of this arrangement has been found to be the significant variability in the cross-section of the air passageway due to typical manufacturing tolerances. For example, the external diameter of the piston may be typically 30.00 mm+/xe2x88x920.10 mm and the internal diameter of the bore typically 30.60 mm+/xe2x88x920.10 mm. Thus, the minimum surface area of the air flow passageway might be 19.04 mm2 and the maximum surface area 38.08 mm2. This represents a variability of +/xe2x88x9233% approximately. Such variability in the cross-sectional area of the air flow passageway results in variability of the force available for operating the apparatus.
According to the present invention there is provided inhalation apparatus for dispensing a product comprising a housing adapted to receive a pressurised dispensing container, and a mouthpiece, a duct for conveying, in use, product from the container to the mouthpiece, valve means movable between a first position in which the duct is closed and a second position in which the duct is open, and a flow sensor being activatable, by means of an airflow created when a user applies suction to the mouthpiece, to move the valve means into its second position, wherein the flow sensor comprises a diaphragm and the diaphragm and/or housing is provided with at least one aperture, wherein the diaphragm comprises a first element connected to the housing and a second element axially slidably movable relative thereto, the first and second diaphragm elements being connected by a flexible member.
In one embodiment the diaphragm comprises at least one aperture.
In another embodiment the housing comprises at least one aperture.
In another embodiment at least one aperture is provided in the second diaphragm element.
Optionally a trigger extends from an exterior of the apparatus into contact with the diaphragm such that operation of the trigger moves the diaphragm axially.
Preferably the trigger is rotatably pivoted on the housing such that one end protrudes through an aperture in the housing and the other end contacts the diaphragm.
Preferably the apparatus further comprises an actuator having a projection, the diaphragm being connected to a tubular guide portion which is axially slidable on a guide surface of the projection to facilitate movement of the diaphragm.
The actuator further defines an actuator chamber, valve seat and outlet nozzle, the tubular guide portion comprising a spigot on which a valve member of the valve means is mounted.
In one embodiment the housing comprises a socket for receiving the pressurised dispensing container, the housing defining at least one port communicating between the socket and the mouthpiece at a location upstream of the diaphragm with respect to the direction of air flow during inhalation.
Typically a pressure drop of between 2.5 and 4 KPa is developed across the diaphragm when an airflow of 50 liters/minute is created by suction on the mouthpiece.
The present invention also provides dispensing means comprising inhalation apparatus in combination with a pressurised dispensing container; said container having a tubular valve stem biased into an extended position and having valve means operable to dispense a metered dose of product through the valve stem when the valve stem is depressed